THICK-KNEES: Burhinidae

PHYSICAL CHARACTERISTICS

Thick-knees vary in size from 12.5 to 23 inches (32 to 59 centimeters) in length and 0.7 to 2.4 pounds (0.3 to 1.1 kilograms) in weight. Their heads are round, their necks are slender, and their bodies are large. Thick-knees have long legs, long tails, and a pointed bill. All thick-knees have large yellow or amber colored eyes and stripes either above the eyes, through the eyes, or below the eyes. Most species are a light sandy brown on top and pale on the belly. The wings are either solid-colored, striped, or spotted while folded. When thick-knees are flying, however, striking black and white patterns on the wings and tail are revealed. Males and females tend to be similar in both size and color. Young thick-knees are colored to blend into their stony or sandy habitats.

GEOGRAPHIC RANGE

Thick-knees are found primarily in the Old World, including portions of Asia, Europe, the Middle East, and Africa. Two species occupy parts of Central America and South America, and several species occur in Australia.

HABITAT

Many species of thick-knees are found in either grassland or brush habitats. Others occupy dry desert areas, usually adjacent to a river or stream. The beach thick-knee is found in seashore areas. One species, the Senegal thick-knee, lives in large cities such as Cairo, Egypt, where it finds appropriate nesting areas on the flat roofs of houses and other buildings. Several species of thick-knees are occasionally found in agricultural lands and pastures.

DIET

Thick-knees have a diet that consists primarily of invertebrates, animals without a backbone, such as beetles, crickets, grasshoppers, crustaceans, mollusks, snails, slugs, and worms, as well as larger vertebrate prey, animals with backbones, such as frogs, lizards, and rodents. Some thick-knees will also eat plant material, including seeds and the shoots of plants. The beach thick-knee eats large numbers of crabs. Thick-knees forage, or search for food, by walking slowly while looking for prey on the ground. Food items are picked up using their strong bills. Larger prey are broken into pieces if necessary before swallowing.

BEHAVIOR AND REPRODUCTION

Some thick-knees, such as the stone-curlew, are generally found alone. Other thick-knees are often found in small groups. All thick-knees spend the majority of their time on the ground, usually perching no higher than a few feet off the ground. However, thick-knees are strong fliers and will fly away if disturbed by intruders. Many species of thick-knees are nocturnal, quiet by day and active at night, when they call loudly.

NOCTURNAL BIRDS

Many thick-knee species are crepuscular (kri-PUS-kyuh-lur; active at dusk) or nocturnal (active at night). The bold, black-and-white wing and tail markings that characterize thick-knees are easy to see in fading light. Because they are nocturnal, thick-knees also defend their territories using loud calls, rather than the visual postures and displays used by other bird species. Their calls are loud and carry a long distance, and thick-knees have become an important part of the folklore in parts of their range.

Breeding in thick-knees occurs in the spring, except in the tropics, when it may occur year-round. The stone-curlew is a monogamous (muh-NAH-guh-mus) species, with a single male mating with a single female. Stone-curlews keep the same mate throughout life. Many other thick-knee species are also monogamous, but the breeding system for a few species remains uncertain. Thick-knee nests are simple and formed by scraping the ground. The male and female select the site together by bowing towards a particular spot. The male chooses the final spot, and the female scrapes at the ground with her feet to clear a nest. Twigs, small stones, and leaves may be scattered around the nest site. Often, several nests are built this way by the pair before one is finally chosen.

In most thick-knee species, the female lays two or three eggs at a time. In the beach thick-knee, only one egg is laid. The eggs are usually light brown in color and either spotted or streaked to make them less visible on the ground. Both male and female incubate, or sit on, the eggs. Eggs hatch after twenty-four to twenty-seven days. The parents immediately move the eggshells away so that potential predators will have a harder time locating the chicks. Thick-knee chicks are able to leave the nest before they are a day old. However, parents continue to protect and to help feed the young. Adults scare off potential predators by fanning their wings and tail. Thick-knee young become mature and capable of breeding after two or three years.

THICK-KNEES AND PEOPLE

Thick-knees appear in Australian folklore, where they have been given names that sound like their calls, such as "weeloo" or "willaroo." One species, the double-striped thick-knee, has been kept in farms and other human settlements to reduce the number of insects.

CONSERVATION STATUS

In Europe, stone-curlew populations have declined due to habitat destruction for agricultural development. Peruvian thick-knees are also declining in their habitats due to human disturbance. Bush thick-knees in Australia have declined due to habitat loss as well as hunting, egg collection, and predation, hunting, by foxes.

BEACH THICK-KNEE (Esacus magnirostris): SPECIES ACCOUNT

Physical characteristics: The beach thick-knee is the largest species of thick-knee and ranges from 21 to 22.5 inches (53 to 57 centimeters) in length. It has thick yellow legs, a long, strong, bill, and yellow eyes. The beach thick-knee is gray-brown on the back and pale on the belly. The shoulder is black above a thin white line. The head is mostly black, with a white stripe through the eye. The bill is black except for a yellow base. There is a rust-colored patch under the tail.

Geographic range: The beach thick-knee is found in the Andaman Islands, the Philippines, Indonesia, New Guinea, other Southwest Pacific islands, and the northern coast of Australia.

Habitat: The beach thick-knee is found on seashore beach habitats. These include sand, shingle, rock, and mud beaches.

Diet: The beach thick-knee eats crabs primarily, but also eats other crustaceans. Large crabs are torn into small pieces before they are swallowed. It generally follows its prey quietly, and then suddenly lunges and grabs. Sometimes, beach thick-knees also search in mud and sand for prey.

Behavior and reproduction: Beach thick-knees fly away when disturbed, usually over the water. Beach thick-knees are monogamous. The nest is usually a shallow depression that is sometimes surrounded by a ring of leaves. The female lays only one egg at a time. The egg hatches after thirty days. The chick is able to fly after twelve weeks, but may stay with its parents for as long as a year.

Beach thick-knees and people: No significant interactions between beach thick-knees and people are known.

Conservation status: The beach thick-knee is not currently considered threatened. However, habitat loss and disturbance may be a problem as beaches become more regularly used for human recreation. ∎

FOR MORE INFORMATION

Books:

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.

Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.

Web sites:

"Burhinidae (Thick-knees)." The Internet Bird Collection. http://www.hbw.com/ibc/phtml/familia.phtml?idFamilia=58 (accessed on May 3, 2004).

"Family Burhinidae (Thick-knees)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Burhinidae.html#Burhinidae (accessed on May 3, 2004).

"Thick-knees, Stone-curlews." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/burhinidae.html (accessed on May 3, 2004).